1. Field of the Invention
The present invention relates to a digital image reading apparatus such as an image scanner that is used in connection with external devices including a host machine, such as a personal computer, a printer, and so forth.
2. Discussion of the Background
Generally, this kind of digital image reading apparatus includes an interface unit that conforms to a SCSI (Small Computer Standard Interface), which is a known popular interface for interfacing external devices.
An original document reading speed of such a digital image reading apparatus that uses the SCSI interface unit to transfer image data to the external device is determined according to a preset reading density. On the other hand, when the digital image reading apparatus transfers the image data upon reading an original document at a reading speed, the data rate for the image data to the external device is determined according to the data processing speed of the external device.
Accordingly, when transferring a certain amount of image data which is defined by reading density and an area to read, the digital image reading apparatus may not have a delay in transferring the image data to the external device if the data rate is faster than the reading speed. However, if the data rate is slower than the reading speed, the digital image reading apparatus is required to have an image memory made of a DRAM (dynamic random access memory) or the like into which the image data is temporarily stored so as to be transferred to the external device free from the fast reading speed but in synchronism with the data processing speed of the external device.
For this reason, the digital image reading apparatus is generally configured to perform the following two operations in parallel when transferring the read image data to the external device. One operation is to temporarily store the image data read by the digital image reading apparatus into the image memory made of DRAM or the like. The other operation is to transfer the image data from the image memory to the external device.
However, when the speed of storing the image data into the image memory is faster than the speed of transferring the image data to the external device or when the reading density is relatively high, an amount of the image data accumulated in the image memory will gradually be increased. In this case, the reading operation needs to be stopped before the image memory is filled with the image data.
In the digital image reading apparatus, a stepping motor is generally used as a driving motor for the image reading operation. Since the stepping motor cannot be stopped instantaneously due to its operational characteristic, a so-called xe2x80x9cthrough-downxe2x80x9d operation, which is a control method for gradually slowing down the driving motor, is adopted. During the time of temporary stop of the reading operation made by the through-down operation, the digital image reading apparatus continues to transfer the image data accumulated in the image memory. When a sufficient amount of the image data accumulated in the image memory is transferred to the external device, the digital image reading apparatus drives the driving motor so as to restart the reading operation. At this time, since the drive motor cannot be started instantaneously due to its operational characteristic, a so-called xe2x80x9cthrough-upxe2x80x9d operation, which is a control method for gradually speeding up the motor, is adopted.
Therefore, when the data rate between the digital image reading apparatus and the external device is relatively slower than that of the image data storing operation, the digital image reading apparatus that includes the SCSI interface unit as standard equipment may need to perform the through-down and through-up operations a number of times during one reading operation. As a result, image quality will be reduced in this case since quality of the image read in a constant speed is better than that read with a number of through-down and through-up operations. That is, a high quality image cannot be obtained by reading the image under a condition of intermittent operations of the drive motor. The number of occurrences of the through-down and through-up operations can be decreased by, for example, extending the capacity of the image memory such as DRAM. However, in this case, the user needs to bear an additional cost due to the extension of the image memory.
In light of the above problems, an object of the present invention is to provide a novel digital image reading apparatus that is capable of controlling a driving motor to reduce the number of through-down and through-up operations during a reading operation with a relatively low cost increase.
To that end, the novel digital image reading apparatus of the present invention includes a reading device which reads an original document to obtain image data; a sub-scanning speed setting device which selectively sets a reading speed of the reading device in a sub-scanning direction; a data transfer device which transfers the obtained image data to an external device connected with the digital image reading apparatus with a communications device; a data rate adjusting device which determines a data rate between the digital image reading apparatus and the external device through a communications operation with the external device; and an image parameter setting device which sets at least one parameter relating to a read image on the basis of the communications operation with the external device, wherein, the sub-scanning speed setting device sets the reading speed of the reading device in the sub-scanning direction according to a value of the set parameter(s) relating to the read image determined by the image parameter setting device.
The sub-scanning speed setting device of the digital image reading apparatus of the present invention may set the reading speed of the reading device in the sub-scanning direction in accordance with a value of the parameter related to a main scanning area.
The sub-scanning speed setting device of the digital image reading apparatus may set the reading speed of the reading device in the sub-scanning direction in accordance with a value of the parameter related to a resolution in the sub-scanning direction.
The sub-scanning speed setting device of the digital image reading apparatus may set the reading speed of the reading device in the sub-scanning direction in accordance with a value of the parameter related to whether the image data is binary-valued or multiple-valued.
The sub-scanning setting device of the digital image reading apparatus may set the reading speed of the reading device in the sub-scanning direction in accordance with plural parameter values related to the main scanning area, to the sub-scanning area and/or to whether the image data is binary-valued or multiple-valued, respectively.
The communication device of the novel digital image reading apparatus may conform to a SCSI standard.